Indium tin oxide (ITO) is extensively used as material for transparent electrodes in such applications as liquid crystal displays, organic light emitting diodes, touch panels, electronic paper, plasma display devices and solar cells. Because ITO has limited flexibility, is costly, has limited transmittance and is applied by such techniques as physical vapor deposition, electron beam evaporation or sputter deposition techniques, new materials are being sought to replace ITO particularly in flexible, low cost applications.
Many elegant attempts at a solution to this problem have been put forth including carbon nanotubes conductive coatings, films of graphene, aluminum, gallium or indium doped zinc oxide, and inherently conductive polymers. While each improves one or more issues, each presents its own set of problems and challenges. For example, fabricating conductive lines and matrices with conductive polymers is difficult.
One approach to replacing ITO is to provide silver thin films which provide excellent conductivity and transparency, flexibility, are readily available and can be coated by a number of cost-effect techniques including printing techniques such as lithography, inkjet printing, screen printing and letterpress.
Some electronic devices, including batteries and electrochemical solar cells, including dye sensitized solar cells, contain liquid electrolyte materials which in many cases can be extremely corrosive to metals used as electrodes for the devices. Some metals and metal alloys, such as Ti foil or ITO, respectively, are not corroded by liquid electrolytes, but ITO replacement materials generally are susceptible to such attack. As a result adoption of non-ITO materials has been restrained in these applications due to the incompatibility of corrosion sensitive materials used as electrodes and the corrosive liquid electrolyte materials.
For example, in dye-sensitized solar cells, a dye is used to absorb light and initiate a rapid electron transfer to a nanostructured, nanoporous oxide film such as anatase TiO2 which in turn transfers the electron to a non-ITO metal conductor attached to a substrate. Charge balance and transport is achieved by an electrolyte layer having a redox couple such as iodide/triiodide (PIO in a liquid carrier such as acetonitrile. The electrolyte is corrosive and can permeate the nanoporous oxide to attack and/or dissolve the non-ITO metal conductor.
Additionally, many of the processes used in the manufacturing of electronic devices, such as solar cells, use highly toxic materials as well as high VOC coatings which add to the cost and place an unhealthy demand on the environment.
As can be readily seen, there is a need for low cost materials for electronic devices which allows for flexibility, cost reduction and ease of manufacture, while at the same time eliminating the problem of liquid electrolyte attack on the conductive metal. Additionally there is an unmet need to reduce environmental pollutants and the use of toxic materials in the manufacture of electronic devices such as photovoltaic solar cells.